Modern mobile cellular telephones are able to provide conventional voice calls and data calls. The demand for both types of calls continues to increase, placing increasing demands on network capacity. Network operators address this demand by increasing their capacity. This is achieved, for example, by dividing or adding cells and hence adding more base stations, which increases hardware costs. It is desirable to increase network capacity without unduly increasing hardware costs, in particular to cope with unusually large peak demand during major events such as an international football match or a major festival, in which many users or subscribers who are located within a small area wish to access the network at one time.
When a first remote station is allocated a channel for communication, a second remote station can only use the allocated channel after the first remote station has finished using the channel. Maximum cell capacity is reached when all the allocated channels are used in the cell. This means that any additional remote station user will not be able to get service. Co-channel interference (CCI) and adjacent channel interference (ACI) further limit network capacity and will be discussed below.
Network operators have addressed this problem in a number of ways, all of which require added resources and added cost. For example, one approach is to divide cells into sectors by using sectored, or directional, antenna arrays. Each sector can provide communications for a subset of remote stations within the cell and the interference between remote stations in different sectors is less than if the cell were not divided into sectors. Another approach is to divide cells into smaller cells, each new smaller cell having a base station. Both these approaches are expensive to implement due to added network equipment. In addition, adding cells or dividing cells into smaller cells can result in remote stations within one cell experiencing more CCI and ACI interference from neighboring cells because the distance between cells is reduced.